2D graphics manipulation

GIMP

Beginner tutorials

PDF - Texturing for Dummies. Somewhat geared towards Photoshop but mostly explains methods and theory. The file is 7.4 MB so you may want to right-click and save this one to view instead of opening it through your browser.

Non-Oblivion-specific tutorials

Modeling Joan of Arc by Michel Roger - This tutorial covers modeling starting with a person all the way through to adding armor, a weapon, UV mapping, rigging, etc. In other words, it's pretty thorough.]